1. Field of the Invention
The invention relates to a process for the preparation of materials crosslinkable with elimination of alcohols to give elastomers, i.e. RTV-1 materials, with the use of hydroxyl-terminated polydiorganosiloxanes.
2. Background Art
Processes for the preparation of materials crosslinkable at room temperature on admission of water have long been known. Typically, such materials are formulated substantially from organopolysiloxanes having at least two hydrolyzable radicals such as alkoxy groups, crosslinking agents having at least three hydrolyzable radicals, again often being alkoxy groups, and catalysts such as organotin compounds. The siloxanes used as base polymers, which are “blocked” at the end, are prepared by a so-called “endcapping” process.
Endcapping is essential for the preparation of RTV-1 materials crosslinkable with elimination of alcohols. The endcapping can take place in several ways: 1) direct compounding with organopolysiloxanes having terminal OH groups employing titanium catalysts; 1.1) in situ endcapping with orthophosphoric esters in combination with chalk, as described, for example, in DE-C-19507416; 1.2) in situ endcapping of organopolysiloxanes having terminal OH groups with the use of (alkoxy)Si—N compounds and combinations of Lewis acids and amine compounds, as described, for example, in EP-A-137883; and 1.3) in situ endcapping with the use of trialkoxysilanes and carboxamides or salts thereof, as disclosed in EP-A-304701; thereafter, the materials are further compounded. 2) Separate preparation of special polymers which are endcapped. 3) Compounding of hydroxyl-terminated organopolysiloxanes with alkoxysil(ox)ane and solid catalysts at elevated temperature, the solid catalysts being subsequently removed, as described, for example, in U.S. Pat. No. 3,383,355.